CN113260804A

CN113260804A - Method for manufacturing a metal ring of a ring set of a drive belt for a continuously variable transmission

Info

Publication number: CN113260804A
Application number: CN201980085902.0A
Authority: CN
Inventors: B·彭宁斯
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2018-12-24
Filing date: 2019-12-24
Publication date: 2021-08-13
Anticipated expiration: 2039-12-24
Also published as: CN113260804B; JP2022515264A; WO2020135928A1; NL1043109B1; WO2020135928A8

Abstract

The invention relates to a method for producing a metal ring (41) for a ring set of a drive belt for a continuously variable transmission, wherein, in a rolling process step, the metal ring (41) extends solely in the circumferential direction thereof while its thickness is reduced. The rolled metal rings (41) are further processed, a plurality of the so processed metal rings (41) being nested one within the other to form a ring set. According to the invention, after the plurality of metal rings (41) are rolled, but before they are nested to form a ring group, the metal rings (41) are turned inside out in a new additional process step (NPS).

Description

Method for manufacturing a metal ring of a ring set of a drive belt for a continuously variable transmission

Technical Field

The present disclosure relates to a method for manufacturing a metal ring of a ring set of a drive belt for a continuously variable transmission, and a drive belt comprising such a ring. Such a drive belt is known, for example, from british patent GB1286777(a) and more recently international patent publication WO2015/177372(a 1). This known drive belt comprises a plurality of mutually nested endless flexible metal bands or rings (i.e. they are stacked concentrically on top of each other in a set or ring group), and a plurality of metal transverse segments arranged in substantially continuous rows along the circumference of such a ring group. Each transverse segment defines a central opening defined by and between the base of the transverse segment and two cylindrical portions extending respectively radially outwardly from respective axial sides of the base, the respective circumferential segments of the ring set being received in the central opening while allowing the transverse segments to move, i.e. slide along the circumference of the ring set. In order to contain the ring set in the central opening, the central opening is partially closed in the radially outward direction by respective axial extensions of at least one cylindrical portion or possibly of two cylindrical portions. In particular, such axial extension of the respective cylindrical portion extends partially above the ring set towards the other, axially opposite cylindrical portion of the transverse segment, and is denoted hereinafter as hook of cylindrical portion.

Background

In the above and in the following description, the axial, radial and circumferential directions are defined with respect to the drive belt when placed in a circular posture. The transverse segments have thickness and thickness dimensions defined in the circumferential direction of the drive belt, height and height dimensions defined in the radial direction of the drive belt, and width dimensions defined in the axial direction of the drive belt. The thickness direction and the thickness dimension of the ring set and its individual rings are defined in the radial direction of the drive belt, the width direction and the width dimension of the ring set and its individual rings are defined in the axial direction of the drive belt, and the length direction and the length dimension of the ring set and its individual rings are defined in the circumferential direction of the drive belt. The up-down direction and the up-down position are defined with respect to the radial or height direction.

In a continuously variable transmission, a drive belt is wrapped around and in frictional contact with two pulleys, each defining a V-shaped groove of variable width, with a respective portion of the drive belt being retained within the pulley V-groove at a variable radius. By changing this belt radius at the drive pulley, the speed ratio of the transmission can be changed. Transmissions of this type are well known and are commonly used in the drive train of passenger cars and other motor vehicles.

The above-described drive belt is distinguished from another known design in which each transverse segment defines two lateral openings, one at each side of a central portion of the transverse segment or of a neck portion between and connecting the bottom or body portion of the transverse segment and the top of the head portion. This type of drive belt comprises two sets of nested rings, each set being received in a respective lateral opening of a transverse segment. In the latter known design, which is known for example from WO2015/097293, the two ring sets are each much narrower than the single ring set of the drive belt described above.

The basic set of overall manufacturing processes for such belts is also well known. Such a basic arrangement is described, for example, in WO2018/122397, particularly with respect to a ring set. The known manufacturing process requires a large number of intermediate steps and these steps are performed within very small tolerances to obtain a high quality end product with excellent fatigue strength. One of such intermediate process steps is the rolling of rings, in which their thickness is reduced and their diameter, i.e. circumferential length, is increased by rotating the ring in its circumferential direction while compressing it between a pair of rolls. For example, the thickness of the semi-finished ring product before rolling is 0.4 mm, and then the thickness is reduced to 200 to 150 μm in the rolling. Such a ring rolling process step is described in detail in WO 2004/050270.

Disclosure of Invention

With regard to this known drive belt and the known manufacturing process, it was found to be surprising. That is, according to the present disclosure, the fatigue strength of the rings-and thus the service life of the drive belt as a whole-can be unexpectedly improved by introducing a new process step that is simple, straightforward and easy to implement. In particular, the improvement is achieved by turning the ring inside out after rolling so that its radially inward orientation, i.e. the inner ring surface, changes to its radially outward orientation, i.e. the outer ring surface, and vice versa. In particular, inside-out flipping refers to pushing one axial side of the ring to the opposite axial side of the ring via the radially inner side of the ring, while pulling the other axial side of the ring to the respective opposite side of the ring via the radially outer side of the ring.

While it is not intended nor anticipated that the improvement in fatigue strength of the ring by turning the ring inside out, it appears that the improvement may be explained later as follows. The highest tensile stresses occur at the outer surface of the ring, both during ring rolling and during use of the drive belt in a transmission. This means that during ring rolling, surface defects or flaws, such as (micro) cracks, dents, foreign particles, etc., mostly originate on the outer surface of the ring and/or are more severe than on the inner ring surface. Also, any such surface imperfections on the outer surface of the ring are less detrimental to the ultimate fatigue strength of the ring than imperfections on the inner surface of the ring during use. In this case, by turning the ring inside out after said rolling of the ring, the majority and/or the most severe surface defects are advantageously relocated to the inner surface of the ring before use.

Drawings

The drive belt manufacturing method according to the present disclosure will now be further explained with reference to the accompanying drawings, in which:

FIG. 1 is a schematic illustration of a known transmission including two variable pulleys and a drive belt;

figure 2 shows, in schematic cross-section, two known drive belt types, each provided with a set of nested flexible metal rings and a plurality of metal transverse segments slidably mounted on such ring set along the circumference thereof;

FIG. 3 provides a schematic illustration of a currently relevant portion of a known overall manufacturing process for the drive belt;

figure 4 is a schematic view of a rolling device for rolling a metal ring as part of the overall manufacturing process of the drive belt;

FIG. 5 shows the metal ring after rolling;

FIG. 6 shows a new process step of turning the ring inside out; and

figure 7 shows how the new process step of ring flipping can be implemented in other known manufacturing processes for drive belts.

Detailed Description

Fig. 1 shows the core components of a known continuously variable transmission or CVT which is typically applied in a transmission system between an engine and drive wheels of a motor vehicle. The transmission comprises two pulleys 1, 2 each provided with a pair of conical pulley discs 4, 5 mounted on a

pulley shaft

6 or 7, defining between the pulley discs 4, 5 a substantially V-shaped circumferential pulley groove. At least one pulley disc 4 of each pair of pulley discs 4, 5, i.e. of each pulley 1, 2, is axially movable along the

pulley shaft

6, 7 of the respective pulley 1, 2. A drive belt 3 is wound around the pulleys 1, 2 and is located in a pulley groove for transmitting a rotational movement and an accompanying torque between the

pulley shafts

6, 7.

The transmission typically further comprises an activation device (not shown) which, at least during operation, exerts an axially directed clamping force on said axially movable pulley discs 4 of each pulley 1, 2, which clamping force is directed towards the other respective pulley disc 5 of the pulley 1, 2, so that the drive belt 3 is clamped between each pair of such pulley discs 4, 5. These clamping forces determine not only the frictional forces that can be maximally exerted between the drive belt 3 and the respective pulley 1, 2 for transmitting said torque, but also the radial position R of the drive belt 3 in the pulley groove. These radial positions R determine the speed ratio of the transmission. Transmissions of this type and their operation are known per se.

In fig. 2, two known examples of the drive belt 3 are schematically shown in their cross-sections facing in the circumferential direction thereof. In both examples, the drive belt 3 comprises transverse segments 32, which transverse segments 32 are arranged in a row along the circumference of an annular carrier in the form of one or two sets 31 of metal rings 41. In either example of the drive belt 3, the ring set 31 is laminated, i.e. composed of a plurality of mutually nested, flat, thin and flexible individual rings 41. The thickness of the transverse segments 32 is small with respect to the circumferential length of the ring set 31, in particular so that hundreds of transverse segments 32 are included in the rows thereof.

Although in the figures the ring set 31 is shown as being made up of 5 nested rings 41, in practice, in

most cases

6, 9, 10 or 12 rings 41 are applied in such a ring set 31, each ring having a nominal thickness of 185 microns.

On the left side of fig. 2, an embodiment of the drive belt 3 is shown, which comprises two such ring sets 31, each of which is accommodated in a respective laterally oriented groove of the transverse section 32, which laterally oriented grooves are open towards the respective, i.e. left and right, axial side. Such a lateral opening is defined between the body portion 33 and the head portion 35 of the transverse section 32 on either side of a relatively narrow neck portion 34, said neck portion 34 being disposed between and interconnecting the body portion 33 and the head portion 35.

On the right side of fig. 2, an embodiment of the drive belt 3 is shown which contains only a single ring set 31. In this case, the ring set 31 is accommodated in a centrally located groove of the transverse section 32, which groove faces radially outwards of the drive belt 3. Such a central opening is defined between a base 39 of the transverse section 32 and two cylindrical portions 36, each extending in a radially outward direction from one axial side of the base 39. In this radially outward direction, the central opening is partially closed by a correspondingly axially extending hook 37 of the cylindrical portion 36.

On either side of the transverse section 32 of both drive belts 3, contact surfaces 38 are provided for frictional contact with the pulley discs 4, 5. The contact surface 38 of each transverse segment 32 is angled

Oriented relative to each other, the angle substantially matching the angle of the V-pulley groove. The transverse section 32 is also typically made of metal.

As is well known, during operation of the transmission, the individual rings 41 of the drive belt 3 are tensioned by the radially directed reaction force of said clamping force. The generated ring tension is not constant, however, and varies not only according to the torque to be transmitted by the transmission, but also according to the rotation of the drive belt 3 in the transmission. Thus, in addition to the yield strength and wear resistance of the ring 41, fatigue strength is also an important characteristic and design parameter thereof. Thus, as the base material of the ring 41, a maraging steel is used, which can be hardened by precipitation (ageing) to increase its overall strength, and additionally case hardened by nitriding (gas soft nitriding) to increase the wear resistance, in particular the fatigue strength.

Figure 3 shows the relevant parts of a known manufacturing method of a ring set 31, which is commonly used in the art for producing metal drive belts 3 for automotive applications. The individual process steps of the known manufacturing method are indicated by roman numerals.

In a first process step I a sheet or plate 20 of a maraging steel substrate having a thickness of about 0.4 mm is bent into a cylindrical shape and in a second process step II the meeting plate ends 21 are welded together to form a hollow cylinder or tube 22. In a third step III of the process, the tube 22 is annealed in the furnace chamber 50. Thereafter, in a fourth process step IV, the tube 22 is cut into a plurality of rings 41, which are subsequently rolled into a larger diameter ring in a fifth process step V, while reducing its thickness to typically about 0.2 mm. The ring 41 thus rolled is subjected to a further, ring annealing process step VI to remove the work hardening effect of the previous rolling process step V by recovering and re-crystallizing the ring material in the furnace chamber 50 at a temperature significantly above 600 ℃, e.g. about 800 ℃. At such high temperatures, the microstructure of the ring material is composed entirely of austenite crystals. However, when the temperature of the ring 41 is again lowered to room temperature, this microstructure may transform back to martensite as desired.

After annealing VI, the ring 41 is calibrated in a seventh process step VII by being mounted around two rotating calibration rollers and stretched to a predetermined circumferential length by forcing the rollers apart. In a seventh process step VII of the ring calibration, the ring 41 also typically has a slight lateral curvature, i.e. convexity (crown), and an internal residual stress is exerted on the ring 41. Thereafter, the ring 41 is heat treated in an eighth process step VIII of combined ageing (i.e. bulk precipitation hardening) and nitriding (i.e. case hardening). In particular, this combined heat treatment comprises maintaining the ring 41 in a furnace chamber 50 containing a process atmosphere consisting of ammonia, nitrogen and hydrogen. In the furnace chamber, ammonia molecules are decomposed at the surface of the ring 41 into hydrogen and nitrogen atoms, which can enter the microstructure of the ring 41. These nitrogen atoms remain partly in the microstructure as interstitial atoms, partly in combination with certain alloying elements of the maraging steel, such as in particular molybdenum, to form intermetallic precipitates (for example Mo 2N). These fillers and precipitates are known to significantly increase the wear resistance and fatigue fracture resistance of the ring 41. It is especially noted that this combined heat treatment may alternatively be performed after or before the aging treatment (without simultaneous nitridation), i.e. in an ammonia-free process gas. This separate aging treatment is applied when the duration of the nitriding treatment is too short to complete the precipitation hardening process at the same time.

A plurality of rings 41 so machined are assembled in a ninth process step IX to form a ring set 31 by radial nesting (i.e. a concentric stack of selected rings 41) to achieve a minimum radial play or gap between each pair of adjacent rings 41. It is noted that it is also known in the art to assemble the ring set 31 immediately after the seventh process step VII of ring calibration, i.e. before the eighth process step VIII of ring aging and ring nitridation.

The process step V of rolling the ring 41 is shown in more detail in fig. 4, fig. 4 depicting a known ring rolling device comprising two rotatable back-up

rolls

8, 9, a rotatable roll 10, a pair of rotatable back-up rolls 11 and a rotatable roll 12. The pressure roller 12 acts on a support roller 11, which support roller 11 in turn acts on the first support roller 8 of the two

support rollers

8, 9. The first back-up roll 8 is placed in the centre of the rolling device, while the other second back-up roll 9 is movably received in the rolling device such that it can be moved away from (and back towards) the first back-up roll 8 to apply a pulling force FI to a ring 41 surrounding and mounted on the two back-up

rolls

8, 9. Also, the pressure roll 12 is movably housed in the rolling device so that it can move towards (and away from) the support roll 11 to exert a thrust Fs on the inner side of the ring 41 via the support roll 11 and the first support roll 8. Said thrust Fs is balanced by the reaction force Fr exerted by the roller 10 on the outer surface of the ring 41 opposite the first support roller 8. Other embodiments of ring rolling apparatus are also known. During the actual rolling of the ring 41, the ring 41 is rotated around and by the two back-up

rolls

8, 9 in the rolling direction indicated by the arrow RD in fig. 4, while being compressed between the first back-up roll 8 and the roll 10 by a pushing force Fs and stretched by a pulling force FI.

The ring rolling process (step V) is mainly aimed at obtaining the desired thickness and circumferential length of the ring 41. In addition, at least one of the inner and outer surfaces of the ring 41 in ring rolling may be provided with a surface relief or increased roughness, either or both of the first support roll 8 and the rolling roll 10 being provided with a corresponding (but opposite) relief or roughness. Typically, the surface relief is provided only to the inner surface 42 of the ring 41 by the first abutment roller 8, so that its outer surface 43 is relatively flat and smooth, as schematically illustrated by the hatched lines in fig. 5 (not drawn to scale).

According to the present disclosure, a new process step NPS is added to the overall manufacturing method of the ring 41, in which the ring 41 is turned inside out, as schematically illustrated in fig. 6 with respect to the ring 41, which is initially, i.e. in the ring rolling (process step V), arranged to have a surface relief structure on its inner surface 42. As indicated by the dashed arrow in fig. 6, such a ring inversion (process step NPS) may be achieved by pushing the left side of the ring 41 to the right via the radially inner side of the ring 41, while pulling the right side of the ring 41 to the left around the ring 41. After ring inversion (process step NPS), the surface relief structure is located on the outer surface 43 of the inverted ring 41 a. According to the present disclosure, it was found that such a turned-over ring 41a, after being turned inside out (process step NPS), exhibits an advantageously higher fatigue strength in the application of the drive belt 3 than a ring 41 which has not been turned inside out after ring rolling.

Fig. 7 shows a preferred embodiment of the above-described new process step NPS, in which the ring 41 is turned inside out in the manufacturing process of the ring set 31. Preferably, the ring inversion (process step NPS) is carried out after the ring annealing (process step VI) instead of immediately after the ring rolling (process step V). In the ring annealing (process step VI), the work hardening of the ring 41 caused by its plastic deformation in the ring rolling (process step V) is removed, so that a lower effort and lower stress levels are involved in the inside-outside turning (process step NPS) of the ring 41. Preferably, the ring inversion (process step NPS) is carried out before the ring calibration (process step VII). After all, in the ring calibration (process step VII), the

rings

41, 41a have a convexity and internal residual stresses, which are defined in particular in the inner and

outer surfaces

42, 43 of the (ring set 31 of the) drive belt 3.

Preferably, all the rings 41 of the ring set/ring sets 31 of the drive belt 3 are turned inside out in order to achieve a maximum increase in the fatigue strength of the drive belt 3 as a whole. However, in order to minimize the influence of the ring flipping process step NPS on the overall manufacturing process, it is also possible to choose to flip only the radially innermost ring 41 of the ring set/sets 31 inside out. After all, such radially innermost ring 41 is usually subjected to the highest stress levels and/or stress amplitudes during operation of the drive belt 3, so that its fatigue strength is most critical for the fatigue strength of the drive belt 3 as a whole. In this case, the radially innermost ring 41 is preferably not provided with the surface relief (as shown in fig. 5) or the surface relief is provided to the outer surface 43 of the ring 41 in the ring rolling (process step V). Thereby, it is avoided that in the ring set 31 the surface relief of the radially innermost ring 41 is in contact with the surface relief of/on the inner surface of the adjacent ring 41.

In addition to all of the details of the above description and all of the accompanying drawings, the present disclosure also relates to and includes all of the features of the appended claims. The parenthetical references in the claims do not limit their scope, but are provided merely as non-limiting examples of the corresponding features. The claimed features may be applied individually, as appropriate, in a given product or in a given process or method, but any combination of two or more such features may also be applied therein.

The invention represented by the present disclosure is not limited to the embodiments and/or examples explicitly mentioned herein, but also includes modifications, variations and practical applications thereof, especially within the reach of a person skilled in the art.

Claims

1. A method for manufacturing a metal ring (41), such as for a drive belt (3), comprising a set (31) of a plurality of such metal rings (41) nested inside one another, wherein the rings (41) are rolled (V) in their radial or thickness direction, characterized in that after ring rolling (V) the rings (41) are turned inside out (NPS).

2. Method for manufacturing a metal ring (41) according to claim 1, characterized in that after ring rolling (V) the ring (41) is annealed (VI) and calibrated (VII), and that after annealing (VI) and before calibrating (VII) the ring (41) is inside-outside flipped (NPS).

3. A method for manufacturing a ring set (31), the ring set (31) being for a drive belt (3) and being assembled from a plurality of metal rings (41) nested one within the other, characterized in that at least one innermost ring (41) of the ring set (31) is obtained by a method for manufacturing a metal ring (41) according to claim 1 or 2.

4. Method for manufacturing a ring set (31) according to claim 3, characterized in that the remaining rings (41) of the ring set (31) are provided with a surface profiling or additional roughness on their radially inner side (42), at least with respect to the radially outer side (43) of the innermost ring (41).

5. Method for manufacturing a ring set (31) according to claim 3 or 4, characterized in that the remaining rings (41) of the ring set (31) are also obtained by a method for manufacturing a metal ring (41) according to claim 1 or 2.

6. Method for manufacturing a ring pack (31) according to claim 5, characterized in that during ring rolling (V) the innermost ring (41) and the remaining rings (41) of the ring pack (31) are provided with a surface profiling or additional roughness on one radial side (42; 43) with respect to the other radial side (43; 42) thereof.

7. Method for manufacturing a ring pack (31) according to claim 5, wherein the ring (41) is provided with a surface profiling or additional roughness on its radial inner side (42).